The present invention concerns a chain link with bushing in a drive chain. The invention also concerns the use of such a chain link.
In connection with conveyor chains by the manufacturing of goods, chain systems are used for conveying holders/containers/trays on/in which the goods are placed during the different production steps.
These chains may be designed in different ways, for sprocket wheels as well as for toothed chains. One of the embodiments, which is widely used, is a roller chain where the chain has great resemblance to chains used for bicycles, motorcycles, etc. In the roller chain the chain pins are fastened, usually riveted, to the outer fishplates while the bushing through which the chain pin is disposed is connected with the inner fishplates. In order to prevent unnecessary wear on the bushing, there is mounted a roller around the bushing.
Other possibilities are the bushing chain, the Gall chain, the Fleyer chain, or toothed chains of different kinds. All link plates are mainly parallel in these chains. A further possibility is the Rotary chain where the link plates are not parallel.
Especially for conveyor chains it is a fact that they have to be laterally flexible to a certain degree so that the chain may run between sprocket wheels disposed in different planes of rotation. This would be difficult if the chains were rigid in the direction of driving. For the chains to be flexible, the bushings are often provided with an inner bushing hole having a cross-section which is made larger than the used chain pins provided through the bushings.
An example is described in U.S. Pat. No. 4,297,839. The chain described in this patent has the primary function of linking a row of wheels used for conveying conveyor units. The principle is not immediately applicable for common conveyor chains running around sprocket wheels.
In order that water does not collect in the interspace between the chain pins and the walls of the bushing holes, a lubricant is often used in the bushings. If a chain for conveyor belts is used for foodstuff production, it is, however, inappropriate that the chain is lubricated with a lubricant as this lubricant, by mixing with dust and the like, under unfavourable circumstances may fall off the chain and contaminate the foodstuff during the process. By foodstuff production, on the other side, if the chain is not lubricated, water may be collected in the assembly bushings of the chain. By the making of freezer goods, like icecream products, where the conveyor runs through a freezer tunnel, the consequence is, in that case, that the chain becomes stiff or that the chain breaks which is a well-known problem and a great drawback.
The object of the invention is to indicate a chain link with bushing for drive chains, preferably conveyor chains, where no water is collected in the bushing of the chain links even if no water repelling lubricants are used.
This purpose is used with a chain link with bushing in a drive chain which is characterised as described in the characterising part of claim 1.
In the chain links for the drive chain, the bushings according to the invention are provided with drain holes wherethrough possible collected water may run out of the bushing. These drain holes may be provided at different places in the bushing, depending of the form of chain and the orientation of conveying of the chain, for example the holes may be provided in the centre or along the rim of the bushing, at the upper side or the lower side of the chain link, or in direction parallel with the direction of advancing the chain. In principle there is no limit to the position and the number of holes in the bushing.
Conveyor chains are often used with the links oriented so that the chain pins are mainly vertical. In such a case it is advantageous to have the holes provided in the lower part of the bushing. In order that the chain may be turned also, the bushings may advantageously be provided with drain holes both in the upper and the lower part of the bushing.
It has appeared that chain links according to the invention with bushing provided with drain hole are particularly applicable to conveyor chains. Since conveyor chains are to be laterally flexible, the hole of the bushing in which the chain pin is disposed is usually made somewhat larger than the chain pin itself. The increased volume between the chain pin and the inner wall of the bushing causes a reduction of the capillary forces so that water more easily runs out of this volume.
In case that the bushing hole of the bushing is circular and has a much greater radius that the chain pin, which is common to known conveyor chains, the contact surface between the chain pin the bushing hole is very small, especially if the contact surface does not extend along the whole bushing hole but only along a partxe2x80x94the contact partxe2x80x94of the hole. This is unfavourable as hereby large surface pressures occurs. In a further development of the invention there is made allowance for this as the contact part, at its front part, is formed with a bending radius corresponding to the radius of the chain pin. In this way the contact surface is relatively great by advancing the chain straightly as the chain pin bears against the face of the contact surface with a relative large part of the surface.
The part of the bushing hole extending through the contact part will be designated contact hole in the following. It is noted that the contact hole may be shorter than the bushing hole itself.
According to a further development of the invention, this contact hole has a cross-section being elongate, for example oval, whereby the chain is laterally flexible.
By forming the elongate contact hole with a width increasing with the distance from the front edge of the hole, a further advantageous function is achieved. In case that all the water is not running out of the bushing, for example if a little water is retained around the chain pin due to capillary forces, by ice formation on the contact surface between the chain pin and the bushing there will be enough space for the chain pin in case of its backwards sliding, whereby breakage of the chain is avoided. The shape of the hole thus performs a number of different functions in combination.
In a further development of the invention, in cases where the drive chain is a roller chain or a bushing chain, there is designed a bushing consisting partly of a tubular bushing part with an inner duct and partly of one or two bushing inserts which are disposed in this duct. The tubular bushing part may be designed as a traditional cylindric bushing known from common roller chains like bicycle chains. The bushing inserts disposed in the inner duct of the bushing are provided with a through-going hole through which the chain pin is provided. The inserts comprise the contact part, i.e. the chain pin is in contact with the bushing inserts and not directly with the inner duct of the bushing when advancing the drive chain. The previously mentioned bushing hole is thereby constituted by the hole through the insert and the remaining part of the inner duct which is not covered by the insert. There are several advantages connected with the bushing inserts.
A first advantage is that the tubular bushing part of the invention may be constituted by the cylindric bushing of steel known from traditional roller chains. The insert then comprises the contact part the hole of whichxe2x80x94the contact holexe2x80x94for the chain pin may be shaped elongate in cross-section so that the contact hole has the advantageous properties described hereinabove. In this way, the making of the chain with chain links according to the invention is relatively simple as only few modifications of existing production steps are required for roller or bushing chains.
The tubular bushing part of the bushing may be cylindric or with other cross-section, for example quadratic. A quadratic cross-section has the advantage that the insert in the bushing will be prevented from rotating in the bushing, thus ensuring that the contact hole of the insert maintains its orientation, also under load and by long-time operation.
Another advantage is that the inserts may be made of a material, for example a polymer having small sliding resistance. Furthermore, the inserts may be made of a material being water lubricating. In this way, wear due to lack of lubrication from conventional lubricants is reduced.
A third advantage is that exactly the inserts constitute the primary wear parts on the chain. When the inserts are worn out, the chain can be disassembled by pressing the chain pins out of the chain links, and new inserts may be provided, whereby the chain may be re-used after assembly. The inserts thus have a cost-saving function with environment-friendly aspects.
A fourth advantage is that the inserts are a relatively small part of the chain which easily may be modified if another shape of the contact hole with the contact surface for the chain pin is desired.
In a further development, by roller chains and bushing chains having inner and outer fishplates, the chain link according to the invention is provided with inserts having a collar extending from the inner duct to and around the edge of the inner fishplate and extending in the interspace between the outer fishplate and the inner fishplate. This collar prevents that the insert rotates in the inner duct in the tubular bushing if this duct is cylindrical. Furthermore, the collar reduces the friction between the inner and the outer fishplates if the collar is made of a friction reducing and/or water lubricating material.
For the chains used with an orientation so that the chain pins are vertical, a drain hole in the bushing is advantageously provided in the insert. The collar ensures the existence of a certain distance between the inner and the outer fishplates where the water may run out of the bushing through a hole in the insert.
In an alternative, further development of the invention, the chain pin is enclosed by a closely fitting insert. In this case the bushing hole, which below is designated the contact hole, is constituted by the hole through the bushing part. This contact hole may thus have an elongate cross-section, e.g. oval, whereas the insert enclosing the chain pin has an outer circular cross-section. The front part of the contact hole is designed with an contour, e.g. bending radius, corresponding to the front contour of the insert whereby is ensured a large surface of contact between the insert and the contact hole when running. The elongate cross-section provides for a reduction of capillary forces in the hole and lateral flexibility of the chain.
In a preferred embodiment of the invention, the bushing hole is circular whereas the insert enclosing the chain pin, advantageously of polymer, is elongate. The front contact surface of the insert has bending radius corresponding to bending radius of the front part of the contact hole in order to ensure a large surface of contact. In the longitudinal direction of the chain, however, the cross-section of the insert is shorter than the bushing hole whereby is achieved the same advantages as described above.
In the following, the chain link according to the invention is illustrated as chain link for a roller chain even though the invention may also be used in other types of chains, cf. the above description.